I don’t usually use a brine when I make Tepache, but maybe this is a different recipe.

Oh hey! Sorry for the slow reply, I just noticed the notification . I got mine at a homebrew store, but here they are on Amazon

Water kefir is another good option - one you get the grains rehydrated it makes a new batch every 24 hours or so, and you can referment it with fruit juice to make a fizzy probiotic drink. It’s much easier to get started with than kombucha